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| Home > Publications database > Potential depletion of ozone in the mid-latitude lowermost stratosphere in summer under geoengineering conditions |
| Book/Dissertation / PhD Thesis | FZJ-2021-03477 |
2021
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-563-5
Please use a persistent id in citations: http://hdl.handle.net/2128/28715 urn:nbn:de:0001-2021093005
Abstract: The world's climate is changing, largely because of anthropogenic emissions of greenhouse gases (GHG). Increasing atmospheric GHG concentrations result in global warming, which changes habitats all around the globe. For limiting the risks of global warming, a supporting option could be the application of sulfate geoengineering. The concept of sulfate geoengineering is to inject sulfate aerosols into the stratosphere extenuating the sunlight, which reaches and thus warms the surface of the Earth. In this way, the surface temperature could possibly be kept at today's level avoiding negative consequences of GHG induced global warming. However, sulfate geoengineering is not free of risks and these potential risks have to be explored before the application of geoengineering can be considered. This thesis is aimed at assessing the risk of ozone loss known from polar winter to occur in the mid-latitude lowermost stratosphere in summer as a potential side effect of sulfate geoengineering. These ozone loss processes were further proposed to potentially occur in the mid-latitudes for today's conditions in combination with convective overshooting events transporting water vapour into the dry stratosphere. If these ozone loss processes occur, the UV-exposure in the densely populated mid-latitude northern hemisphere would increase in summer. In this thesis, the chemical ozone loss mechanism in the mid-latitudes and its sensitivity to a variety of conditions is extensively analysed by conducting box-model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS). This analysis shows that a threshold in water vapour has to be exceeded for stratospheric ozone loss to occur. This water vapour threshold is mainly determined by the temperature and sulfate content of the air mass. The extent of ozone loss depends on available chlorine and bromine concentrations and the duration of the time period over which chlorine activation can be maintained. However, a simulation for conditions over North America, which are realistic but selected to be mostsuitable for this ozone loss process, did not show signicant chlorine activation. Moreover, the likelihood for this ozone loss process to occur today or in future scenarios is determined considering both climate change and an additional application of sulfate geoengineering. Therefore, atmospheric conditions causing chlorine activation are determined based on CLaMS box-model simulations and compared with conditions found in the lowermost stratosphere inresults of climate simulations using the Geoengineering Large Ensemble Simulations (GLENS). Extensive sensitivity studies in this thesis show a 2-3 times higher likelihood for chlorine activation in the future scenario with sulfate geoengineering than for today. However, even if geoengineering were applied, the likelihood for chlorine activation to occur above North America remains low (max. $\thicksim$3.3%), destroying less than 0.4% of ozone in the lowermost stratosphere. An upper limit for total ozone column reduction of 0.11 DU (less than 0.1% of column ozone) is deduced in this thesis. Overall, this thesis demonstrates a negligible risk for chlorine catalysed ozone loss to occur in the lowermost stratosphere over North America in summer for conditions today and in future, even if sulfate geoengineering were applied. This is an important contribution to assessing the risks of a potential application of sulfate geoengineering in future.
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